1. Field of the Invention
The invention relates to a system with a three phase superconductive electrical transmission element, in which three superconductive electrical phase conductors are insulated relative to each other and concentrically arranged relative to each other, and which is arranged in a thermally insulated tubular cryostat which has a free space for passage of a cooling medium therethrough (WO 2004/013868 A2).
2. Description of the Related Art
Superconductive cables have in today's technology electrical conductors of a composite material which contains ceramic material which at sufficiently low temperatures changes over into the superconductive state. The electrical direct current resistance of an appropriately constructed conductor is zero with sufficient cooling as long as a certain voltage is not exceeded. Suitable ceramic materials are, for example, BSCCO (bismuth-strontium-calcium-copper oxide) as a material of the first generation or ReBCO (rare earth-barium-copper oxide), particularly YBCO (yttrium-barium-copper oxide), as materials of the second generation. Sufficiently low temperatures for placing such a material into the superconductive state are, for example, between 67K and 90K. Suitable cooling agents are, for example, nitrogen, helium, neon, and hydrogen or mixtures of these materials.
The known system according to the above mentioned. WO 2004/013868A2 has as the transmission element a superconductive electrical cable in which three phase conductors are arranged insulated relative to each other and concentrically relative to each other. With the inclusion of a further insulating layer, a neutral conductor is additionally placed as the fourth conductor around the three phase conductors. The compact arrangement with four conductors of superconductive material is placed in a cryostat and, during operation of the transmission system, is cooled in order to achieve the superconductivity. The individual phase conductors consist of several layers of superconductive bands. The number of bands, and thus, the conductor cross-sections, depend on the power to be transmitted.